Pour sugar into the bottom of a saucepan and turn the heat to medium. Add in the cinnamon sticks. Use a rubber spatula to stir the sugar constantly until it melts and turns a nice caramel color, about 5 to 7 minutes.
Remove the cinnamon sticks and discard. Pour in 1/2 cup of the whole milk. The caramel will seize a little bit, but continue stirring. Slowly pour in the milk, stirring constantly. As the milk heats up over medium heat, the caramel will begin to dissolve.
Once the caramel has dissolved and the milk has heated up, stir in the bittersweet chocolate until melted.
Pour the liquid into a blender. Be sure it is vented out the top so that pressure does not build up and blend for 60 seconds until smooth. Serve hot.